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Journal of Electronic Materials, July 2013, Volume 42, Issue 7, pp 1335-1339.
Yuzuru Miyazaki, Hidenori Ogawa, Takaki Nakajo, Yuta Kikuchii, Kei Hayashi.
Department of Applied Physics, Graduate School of Engineering, Tohoku University, 6-6-05 Aoba, Aramaki, Aoba-ku, Sendai, 980-8579, Japan
Abstract
Polycrystalline samples of misfit-layered sulfides [Ln2S2] p NbS2 (Ln = lanthanides) have been prepared using the CS2 sulfidation method. Except for Ln = Eu and Lu, single-phase samples were prepared. The compounds consist of an alternate stacking of a trigonal prism-type [NbS2] layer and a double-layered NaCl [rock salt (RS)]-type [Ln2S2] block, parallel to the c-axis. Three types of stacking modes of the [NbS2] layer and the RS-type block have been confirmed with a (3 + 1)-dimensional superspace group description: two face-centered orthorhombic structures and one face-centered monoclinic structure. Slightly cation-deficient samples with Ln = Yb exhibit the highest Seebeck coefficient S ≈ 59 uV/K. With electrical resistivity of ρ=1.4mΩ cm and thermal conductivity of κ = 0.69 W/Km, this yields a dimensionless figure of merit of ZT = 0.11 at 300 K.
